1. Field of the Invention
This invention relates to an apparatus for adjusting the tool length of a bending machine in which the effective length of an upper tool can be exchanged to the desired bending length according to the bending width of a sheet metal plate.
2. Description of the Prior Art
Metal plates having each edge of four sides of a rectangular sheet metal bent by at least one or two times are used for cabinets, display cases, bending machines, refrigerators, freezers, air conditioners, computer units, various office machines, etc. To prepare such plates, wiping benders, folding machines or press brakes are used to bend each side edge of a sheet metal previously cut into a quadrilateral. For example, in order to bend each side edge in the U-shaped form, the edge of one short side of the sheet metal is bent by two steps (short side bending) and then, after the sheet metal is turned 180.degree. on a handling table, the edge of the other short side is bent. Next, the sheet metal is turned 90.degree. and the edge of one long side is bent (long side bending) by a clamp die or punch set to the bending width adjusted to the inside of the short side bending. Further, the sheet metal is turned 180.degree. and the other long side is bent so that the rectangular metal plate having the four side bent in the U-shaped form is obtained from the first step bending and the following second step bending.
In the above working, when the long side of the metal is bent, rising portions are produced by bending the previously bent short side, so that the upper die should have the length of the long side obtained by subtracting the thickness corresponding to two sheets and avoid the interference with the rising side of the short side. Thus, a plurality of the upper dies having different die widths are prepared and every time the sheet width is changed, the die is interchanged manually. To overcome the defects caused by such manual operation, an apparatus for adjusting the tool length has been developed in which the upper die can be split while the upper split dies having different die widths are combined such that unnecessary upper dies are retreated or inverted according to the sheet metal length to be adjusted to a desired upper die length. However, since the die length is only stepwise changed by simply putting in and out the upper split dies, it cannot cope with the bending work for various lengths of works, presenting problems of complicating control for changing the die length.
Also, as above mentioned, when the respective side edges of the metal plate are bent in the U-shaped form, since the edges of the short sides are previously bent into the rise having the U-shaped section, the upper corner dies should avoid the interference with this rise to approach the sheet metal. Furthermore, when the die is withdrawn after the U-shaped bending of the long side edge, the upper corner die should not interfere with said rise. Thus, normally, an openable die (or rotary die) is mounted on the upper corner dies disposed on both ends of the upper split dies by the use of a pin. And to pivot this openable die without any troubles, a clearance is provided in an edge portion of the upper corner die body to avoid the contact with the pivotal portion of the openable die. However, since this clearance provides a cut-out portion of the edge line of the upper die, the bending line of the sheet metal has irregularities on the clearance portion so that accurate bending form cannot be obtained.
An object of the present invention is to provide an apparatus for adjusting the tool length of a bending machine in which the tool length can be changed easily and quickly.
A further object of the present invention is to provide an upper bending die in which the edge lines of the lower portion of the upper corner die body and the openable die are interconnected continuously.